5G era will usher to unlimited possibilities and innovation. It will bring a transformation that will alter the canvas of services being offered to customers and change the competitive landscape. The peak data rate for 5G will be a 20 fold increase than the current LTE-A peak data rate, and latency will decrease by tenfold.
The no of connected devices will reach One trillion by 2030, according to Deloitte. This massive no of connected devices needs to be supported by a network that has very little latency. It can be achieved by a split of traditional network architecture and improved transport network.
1 Trillion connected devices look very encouraging from the revenue perspective of Telcos, but monetization of their assets is not all so rosy. Telcos now need to compete not only with their incumbent peers but also with disruptors like OTTs.
OTT operation is very intriguing for Telecos. They use the telco’s infrastructure to provide their services and monetize them, but eat away the core offerings of Telcos like voice and SMS. Just compare the adoption of Whatsapp voice and messaging services with traditional SMS and voice calls. The difference in features and offerings are quite striking between the two. To provide the subscribers, of the OTT platforms with high-quality content, OTTs like Amazon, Google are building up their high-capacity data center and backbone transport network. This is to enable them to bring their content as close as to the access network to support ultra-low-latency. So it is quite obvious for wireless carriers too to build and develop a robust, and highly responsive transport network for 5G. This will help them to fight the competition and also provide more business use cases.
 
For an efficient 5G network to build, wireless carriers need to focus on the disaggregation of their Access Network, introduce virtualization and build an efficient transport network. Disaggregation: Disaggregation of the access network is generally the split of the Access architecture into Centralized Unit (CU), Distributed Unit (DU), Radio Unit (RU), Fronthaul Interface (RU-DU), Midhaul Interface (DU-CU), and Backhaul Interface (DU-Core).
Transport network will encompass among all the interfaces, but transport requirement for backhaul will draw the highest traction. Since 5G use-cases will require low latency and high speed, hence this will be attained by using the spectrum of high frequency. This will essentially mean the densification of the network. Also, all the cell sites need to be connected to a 5G core network with a high-speed backbone. We can have several transmission architectures based on Microwave, Copper, and Fiber, but the 5G benefits can be leveraged by using a Fiber transport network. Challenge for the operator is to find the ideal mix and match between different deployment technologies as the backhaul.
Let us take a quick comparison between different transport mediums for backhaul. As noted in the below table, Fiber comes out to be the most viable option for 5G use-cases in terms of bandwidth. 
 Table: Comparison among different Transport mediums
From a Wireless carrier perspective, 5G deployments, will happen in the Macro Cells site and Small cell site. Macro Cell Site deployment will generally take place in rural areas, whereas small cell deployment will take place in urban and suburban areas. Since the TCO for Fiber (Fixed Backhaul) is higher than Microwave (Wireless Backhaul), it is imperative that during deployment, there will be a mix and match of both fixed and wireless backhaul. The Reason being carriers will try to cost optimize and increase their ROI (Return on investments).
The future of Communication is Wireless, but the future of Wireless is Fixed.
Although fiber provides significant bandwidth, there are several complex technologies that are involved so that there is the optimal usage of the capacity. With time there has been a significant reduction in cost fiber deployment cost with solutions like micro-trenching and fiber optic insertions.
WDM is the technique used in fiber optic communication. It multiplexes several optical carrier signals in a single fiber by using different wavelengths. WDM is divided into three different wavelength patterns. 
Using these technologies of WDM, modern Fiber systems can a handle capacity of 1.6Tbps per fiber. But for the wireless carriers, the major challenge in deploying fiber is cost, logistics, and insertion in underground tunnels. With the inter-site distance becoming less due to the densification of networks the amount of person-hour and operational and maintenance cost in deploying fiber will increase. New business models where fibers can be shared between different operators (railway, wireless carrier) are also up ticking, making economic sense in terms of cost of network deployment. Although there is a significant reduction in fiber implementation with modern technologies, the large-scale deployment of 5G networks will see several other technologies also acting as mobile backhaul.
5G use case requirement and deployment strategies have stimulated the splitting of the NR Radio access into three different segments, fronthaul, Midhaul, and backhaul, as highlighted in the RAN access split diagram. These three tiers of network segment are called X-HAUL or anyhaul. Now this X-HAUL interface will need connectivity options and has motivated towards the development of different Transport gears.
Wireless Mobile backhaul can operate in the below spectrum ranges:
Microwave has been the dominant technology for mobile backhaul for years. Although predominantly used in MACRO cell sites, but its wide operating frequency range can also be used to cater to small cell transport networks too. Lower frequency ranges are generally used for fronthaul or Midhaul scenarios, whereas spectrum bands above 20GHz can be used for Backhaul links.
Higher frequency bands will allow the provision of higher bandwidth. E band and V Band are generally used for radar communicator and research purposes. But recently, some Governments like the US, France, Poland have allocated 80GHZ for wireless backhaul. Microwave deployment for these bands will be mostly restricted for small cell deployments. But migration to these bands is still underway, and the rate of adoption is still at the nascent stage.
The following table highlights the performance metrics of different spectrum bands. As noted in the below table, Fiber comes out to be the most viable option for 5G use-cases in terms of bandwidth.Â
Fiber and Microwave are the two predominant backhaul connectivity choices for 5G deployment with each having its pros and cons. With commercial deployments happening for mmWave, a new wireless backhaul solution, Integrated Access Backhaul (IAB), is introduced by 3GPP from Release 16. In IAB, the NR radio uses part of the radio spectrum for backhaul connectivity. Although IAB can operate in any frequency band but from a deployment perspective, to maintain network quality mmWave is ideal. IAB can use the same frequency that is used for access for backhaul, or it can also have different frequencies for access and backhaul.
IAB has got some prerequisite conditions for implementation
IAB donor is a gNB that is directly connected to a backhaul by fiber and provides network access to UE and wireless backhaul connectivity to other IAB nodes. The IAB donor connects with the IAB node using the New Radio access interface and communicates over the FI interface. The Routing functionalities are performed by BAP (Backhaul Adaption Protocol).
IAB node connects with IAB donor and subsequently connected to another IAB node. It provides radio access to UE and backhaul connectivity to the downstream IAB nodes. The IAB can use a separate antenna called Mobile Termination (MT) for Backhaul traffic, or it can share its access antenna for Backhaul Traffic and UE traffic.
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